Method of heat treating and heading bolts



Jan. 10, 1928.

C. A. HOAG METHOD OF HEAT TREATING AND HEADING BOLTS Filed Oct. 1, 1925 lll MK T 25h BBK QMDOQU NQ @Sub Patented Jan. 10, 1928.

VUNITED STATES PATENT OFFICE.

CHAUNCEY A. HOAG, OF JACKSON, MICHIGAN, ASSIGNOR, BY MSNE ASSIGNMENTS,

TO KELSEY-HAYES WHEEL CORPORATION, F DETROIT, MICHIGAN, A CORPORA- TION 0F NEW YORK.

Application led Qctober 1, 1925. Serial No. 59,842.

, This discovery relates to the method of manufacturing bolts. It is the object of the method to make a bolt of the best possible quality and to do so more economically than has been done previously. These accomplishments will be apparent after a detailed description is given of the .old commercial practice, and the present improved method. x

The drawing shows a diagrammatic View indicating the several operations and the sequence.

The practice in bolt manufacture 1s to feed the rod stock through a heating furnace, thence through a. headingv machine Wh 1ch forms the head on the stock by a forglng or upsetting operation, and cuts off the stock at the proper length. The work is then put through `a. tumbler and then through a pointing machine, and finally through a threading machine. i

However, it is found necessary in practice to buy oversize stock so that it can be drawn down slightly to get stock which better a proximates the required accuracy. This cod drawing operation may result in certain cold Working effects or changes 1n the metal structure which make the resulting bolts relatively hard and brittle. This has, in a measure, been appreciated and the condition has been largely corrected by proper heat-treating of the bolts in separate furnaces and allowing the same to cool, either by slow cooling or by rapid cooling, such as quenching. This serves to remove the bad effects due to the cold working by effecting .a more or less complete structural change in the steel. A rapid cooling operation Will also materiallyr harden the bolt and improve its quality. So far as I am apprised, it has been the practice to do this heat-treating after the bolts have been pointed and threaded.

One of the objects of the present invention is to perform the heat-treating and cooling operation before the pointing and threading operation. By changing the sequence of these operations it is found that a very much improved bolt results for the reason that there :is presented a stock of more uniform structure to the pointing and threading tools. The stock, after it has been drawn down to the proper dimensions and placed in a coil to be fed to the furnace, varies considerably due to manufacture of the stock by the mill, and the cold Working effects that may result in the stock due to the action of the reducing and sizing dies. In ordinary forging or hot heading practice, these effects are not removed. On the contrary, additional structural distortion is incurred in the upset portions for the reason that the steel is below the critical temperature. The consequence is that stock in this condition is found non-uniform in machinability when presented to the pointing dies and threading tools. Some of the stock may be relatively hard and resist the cutting operations, While otherstock may be comparatively soft and cut deeper, consequently is cut under-size. Also. hard stock very often results in excessive tool breakage. It has been found that the machines can be safely run at greater speed in threading and pointing the bolts Where the bolt has been heat-treated than they can be run with bolts that are not heat treated until after this threading and pointing operation.

Still another result of my process that I find advantageous is that the threads are clean; Heat-treating always leaves more o1" less scale. This scale, in my process. is removed before the threading and pointing, While in the common practice of heat-treating a threaded and pointed bolt the scale, of course, remains on the finished bolt, or is removed by tumbling which injures the threads. It has been customary to accomplish this heating in a rotary furnace in which the bolts tumble from one end of the furnace to the other. This. of course. tends to injure the threads. The common practice of quenching in oil leaves the threads covered with scale.

It is also not possible in heat-treating these bolts in large aggregates and masses in a furnace to control the temperatures for the separate pieces of stock and get uniformity. Therefore. as I view it, advantageous and unexpected results follow the treating of the Work before the threading and pointing operation. This heat-treating operation in its more general application could, of course, be carried out by separate hea-ting and cooling. However, I prefer to carry out this heat-treating operation in a way that I believe to be new in bolt manufacture, and which has manifest advantages over a reheating operation.

I propose to use a single heating for preparing the stock for the forging operation 'and the heat-treating operation. 'One advantage is that it results in a great saving in plant equipment, and a large saving 1n fuel and labor. I have found that by raising the temperature of the wire stock as 1t passed through the furnace, say by from two'hundred to three hundred degrees above common hot heading practice, that this does not injurio'usly affect the forging operation, yet a temperature isl reached which will cause a change in the structure of the metal and eliminates the cold working effects.

If the stock is thenfquenched in water kept at uniform temperature, for steel of like composition, quite remarkable results are accomplished in the uniformity and improved quality of the bolts.

Il have illustrated in the diagrammatic showing of the method, how the rod stock is contained on a coil, passes through the furnace, thence into the heading and cutting machine; from there it drops into the water, which is preferably kept at a uniform tem- V parat-ure by thermostatic control valves that let out the hot water and let in more cold water; the blanks drop into conveyors at the bottom of the tank and are carried out by these conveyors so that they do not accumulate at the bottom of the tank; thence the stock is assed to a tumbling drum to remove the sca e, and finally it is pointed and threaded.

I regard the cont-rol of the water in the.

tank as quite important as it is desirable to have a uniform temperature in order to get uniform results, and of course the automatic cont-rolv` of temperature is very reliable. I

have, also, found that small changes in the temperature of the water, for instance, fifteen degrees, bring about -considerable change in. the character of the finished bolt. Of course, the water temperature is varied to accommodate different heats 'of steel which '.vary in composition and ability to harden, so as to secure a rapidity of quenching which shall yield belts of standard hard.

ing, also for effecting theheat-treating operation. Furthermore, as already intimated above, I am able to control the'heat-treating of the stock in a way that is not possible where the heat-treating is done with the stock after it has been cut up, for then it hasto be treated en masse. In such a mass 7some of the separate pieces are heated more than others, the consequence is that the results are not uniform. On theother hand, by my method where the stock passes through the furnace simply as rod stock, it is possible to control the heat of the stock within nice limits by controlling the heat of the furnace and the rapidity of travel of the stock. I, therefore, regard the controlled heating'of the stock for heat-treating effects at the same time as prepared for forging as a very important improvement in this art, producing a much higher grade of bolt and making a considerable saving in opera"on.

The-re are several ways that the desired temperature of the traveling rod stock may be obtained. One of these ways is to run the heading machines at substantially their full capacity, and to heat up the furnaces to about 2600 degrees Fahrenheit. rIhis, however, is very destructive to the furnaces, as this temperature is about the slagging point of fire brick, and it is further found uneconomical in' fuel to run at such temperatures. Furthermore, this temperature results in a quick heating of the s tock, and there is considerable difference between the center and outside of the stock in temperature. This has disadvantages, for it leaves the outside softer than desirable when the 1625 to 1650 degrees is secured at the center, and when the stock` reaches the heading dies this soft outside stock is so plastic that it often squeezes in between the dies and forms an objectionable fin on the bolt; and furthermore, by reason of being considerably hotter than necessary on the exterior the stock tends to draw the temper of the dies.

In view ofthese facts, I consider it desirable to get the required control of the temperature by methods which are not conducive to the early destruction of the furnace, and which will not tend to establish too great a differential in temperature between the exterior and the interior of the stock. There are several ways that this may be accomplished. One of them is to run the heading machines at their full capacity and quite materially lengthen the furnaces. Another method is to materially lesseni the Vspeed of travel of the stock and decrease the capacity of the heading machines. Another way is to heat a whole coil or a large part of a coil at one time so that any given point in the coil is Within the furnace for a considerable period of time. Another way, which is found the most advantageous, is to lll keepthe heading machines at their full capacity and use a furnace of substantially i the old dimensions, i. e., twenty to thirty feet long and feed the stock through in two lines for one heading machine. 'llhis last method is not( described in detail here--it is omade the subject matter of,a copending application tiled by Walter Gairing, Serial No. 66,716., tiled Nov. 4, 1925.

My method has heen .described particularly in connection with the manufacture of bolts, but obviously has a wider application.

vIt is, therefore, not to be understood as limited to holts., lout to cover similar articles under similar conditions. Therefore, wherarticles, the steps which comprise coincidentally heating the continuous rod stock for both the forging operation and for heattreatingl the stock to eliminate cold working or other effects, and heading the work.

2. In the manufacture of bolts or similar l articles, the steps which comprise the heating of the stock initially while in continuous rod form to a temperature considerably in excess of the temperature necessary for `the forging operation and at a temperature calculated to secure heat-treating effects to `eliminate cold working or other e'ects, then while the stock is in such condition heading the same.

3. Inthe manufacture of bolts or similar articles, the steps which comprise the heating of the rod-like stock to approximately 1625 degrees Fahrenheit, then heading the stock.

4. In the manufacture of bolts or similar articles, the method which comprises the heating of the rod-like continuous stock relatively slowly to a temperature considerably in excess of the necessary forging temperature, the slow heating being such as calculated to lessen the differential of the temperature between the outside and inside of the stock and the excess temperature referred to being such to eliminate the cold working or other eHects, and heading the stock while inV such condition.

In testimony whereof I have aiiixed my signature.

CHAUNCEY A. HOAG. 

